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Dual battery systems.


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Hi guys, iam going to put a dual battery systems in my 2015 Gu Patrol but there are so many Battery Isolator out there I don't no witch on to use. Can you recommend any proven types that you guys are using.

Ive had a dual battery set up in GQ patrol that was just a solenoid witch ran the batterys in parrell this worked fine for yrs but iam not sure about doing this with the newer patrols.

Ill be running 75ltr Engel fridge,x2 12volt outlets.

Found a good battery tray with a heat shield to help keep battery temp down from turbo heat from Off Road Down under Dual Battery Trays,  as I have cooked a battery in my old GQ patrol once from the Engine/turbo heat, fixed this buy installing a bonnet scoop.

Any help would be appreciated






Edited by Paul
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Welcome to the jungle mate!

The issue with dual batteries and how to connect them is complex becuase a lot depends on type of batteries, usage and charging method employed. Here is my take on it.

The most basic system would be to have voltage sensitive relay/switch which disconnected aux/second battery when voltage drops bellow preset level.

The vehicle alternator does all the charging and doesn't really do the best job but tries.

The proble in here is that 2 different battery types are usually employed; starter type and deep cycle type.

Both have different requierement for charging/discharging hence vehicle alternator struggles to pick which one so the quickest one to be charged  gets all the glory, usually starter batery. 

So typical solution to this problem is thave the second battery completely separate from the vehicle charging system and being charged via DC to DC charger.

Good points: second battery is always properly charged subject to certain caveats and no complex heavy wiring required between battery so to speak.

Bad points: DC chargers are slow chargers, so a long cruise trip might be fine to recharge the deep cycle batery after overnight stop but not everyone drives for hours on the 4WD trip.

The best solution is to have hybrid system that is have both VSR switch for short trips and DC charger for long trips as well as supplemented viua solar for those several days/ a week camping stop.

Another point is to have same type batteries which is almost impossible see starter vs deep cycle debate so one vay out of it is to have hybrid batteries whic are both starter and deep cycle in one unit. They're very expensive still but it is the future as more and more manufacturers fit them because the modern carselectrical loads are so varied.

The best way to start is to look at the expected usage with a bit of redundancy trown in to the mix and work from there.

I haven't mentioned the wet lead acid, lead acid calcium and absorbed glass mat (AGM/gel) type batteries, each of those have different charging requirement and quirks. If your car alternator is not designed for example to deal with calcium and AGM units then having just VSR relay is not ideal in fact bad for your investment in those expensive units.

I'd personally give Redarc range a look even though they're bloody expensive. It is still Aussie made. Ctek DC/DC chargers are Chinese made but Swedish designed and half price of Redarc but.....



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Thanks for the input there we will only be using the 2nd battery when the car is running as I never leave the Engels running over night on 12v.

I will be getting the Redarc SBI12kit, which seems to have great reviews from what I have read and supporting aussie made product.

The battery I thought I might get would be a Optima Yellow Top as they recharge quickly and has 700cca if I need it.

One day I might head back up to my old stomping grounds N.T were the roads dirt roads are rough so this battery should work fine.

I want to mount the isolator under the car bonnet to so the Redarc can handle the heat from what ive read.

I use a Redarc tow-pro which has never let me down so I hope the solenoids as the same. 





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Optima AGL/gel battery is completely unsuitable to be mounted in the engine bay, hates heat and vibrations. have a look what type of battery is fitted by Nissan and then fit exactly the same type but deep cycle and try to fit some sort of a heatshield I cooked 4 batteries in 3 years.

Patrol's Y61 spot for second battery is very unfortunate one as it gets heated from both sides (exhaust and header/expansion tank).

Redarc SBI12 is a good unit as long as it is properly installed and earthed. Mount it on the starter battery side (cooler) as well.



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Holly cow..this is why I join a patrol forum..thaxs mate for that info ..the battery tray has a heat shield and the floor is raied so air can flow around battery getting from > Off Road Down Under.

The battery in the new 2015 patrol is encased in a plastic shield which has a air duct which connects into it, draws air from under the front guard.

The car has done only 700km,  so iam trying to get it right 1st time

I have to investigate some more to see what type of battery the put in.

Thank a mil


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Easy, you can get Century N70T deep cycle battery as your second unit. Its same wet type flooded with caps so you can check it yourself with hydrometer as required instead of those MF crap things which indicate green but battery is stuffed....


Also that tray from Downunder is a good find, I also like ==>



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The wife goes to me your from the NT you had dual battery system in both the 4.2d and the 2.8td and I used NZ70 batteries and ran them in parallel threw a solenoid and never had a problem with charging or the heat up there. So funny you should say the Century N70T deep Cycle cause that's what I was just looking at.

We had to run Bridgestone tyres only on our work utes and duellers on 4wd as they could handle the road temps. 

You no the old rule stick to what you no..think I got side track with all the different stuff out there know.

Thanxs again

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